I.C. Engines

ABSTRACT

An internal combustion engine of reciprocating-piston type with injection of liquid or gaseous hydrocarbon fuel, provided with catalytic means for initiating the combustion of the air/fuel charge in the combustion chamber of the or each cylinder. The major part of the combustion chamber of each cylinder is afforded by a recess formed in the piston crown, and a catalytic element of mesh, grid, perforated or sintered or other construction, is carried by the piston in a position at least partly overlying the said recess, the fuel being injected into the said recess to contact and pass through the catalytic element, being ignited by its contact with the catalytic element.

BACKGROUND AND OBJECTS OF THE INVENTION

This invention relates to internal combustion engines of thereciprocating-piston kind, utilising liquid or gaseous hydrocarbonsfuel. The invention, which concerns the ignition of the air/fuel mixturein the combustion chamber of the engine, is particularly, although notexclusively, applicable to reciprocating-piston petrol and dieselengines although it may also be applied to engines utilizing other formsof liquid fuel such as methyl or ethyl alcohols and even gaseous fuels.

With the rising number of road vehicles with i.c. engines in regularuse, particularly in urban areas, problems of air pollution have becomeacute, particularly in certain places having long periods of sunshine,due to photo-chemical reactions between the atmosphere and the exhaustemission of such vehicle engines. This effect manifests itself as "smog"due to complexes of nitrogen oxides, giving rise to reduced visibilityand irritation of the eyes, nose and throat. This had led to theintroduction of legislation in at least one country to limit locally thequantities of unburnt hydrocarbon, carbon monoxide and nitrogen oxidespresent in the exhaust emissions of all road vehicle engines. This legallimitation has hardened progressively with time, to an extent whichposes considerable technical difficulties to vehicle and enginemanufacturers.

One approach to the problem of reducing undesirable exhaust emission isto operate engines with as weak a mixture strength as possible, i.e. ashigh an air/fuel ratio as is practicable, giving a marked reduction inNO_(x) emission with increases in air/fuel ratio but with an increase inHC at high air/fuel ratios. NO_(x) is formed at high combustiontemperatures and once formed remains very stable. However with highair/fuel ratios the rate of combustion reaction is slowed down and lessheat is released from the smaller quantity of fuel used, so that thetemperature rise of the whole air/fuel mass is less than withstoichiometric mixtures. On the other hand the actual burning efficiencyof the hydrocarbon fuel is lowered at high air/fuel ratios due to itsgreater diffusion into the air present, so that although it is possibleto ignite the fuel locally by an intense spark at weak mixtures, theflame often fails to reach all the fuel present and as a result someunburnt hydrocarbons remain in the exhaust gases.

Numerous attempts have been made to overcome this by designing so-called"stratified charge" petrol engines in which the fuel is concentrated ina locally-rich portion of charge in proximity to the spark plug orignition point, and this rich mixture burns rapidly on ignition beforebeing dispersed into the remainder of the charge which may consist ofair only. Whilst some reduction in unburnt hydrocarbon levels in theexhaust emissions has been obtained with this approach, there is stillample room for improvement.

At present, the only two methods of igniting the air/fuel mixture in ani.c. piston engine employed in practice are spark ignition andcompression ignition, each of which relies on the spread of combustionby a flame front throughout the whole of the mixture charge.

An object of the invention is to provide a new and different way ofcatalytically igniting the charge in an i.c. piston engine, which doesnot rely on a flame front to spread the combustion throughout thecharge, and which will enable very weak mixtures to be utilized whichare not burnable by ordinary spark ignition or compression ignitionmeans.

It has been proposed to utilise a catalyst member mounted in thecombustion chamber of the or each cylinder of a piston engine to ignitethe air/fuel charge and so initiate the combustion. The catalyst memberin this proposal takes the form of a relatively thick disc of honeycombstructure fixedly mounted in the cylinder to extend completely acrossthe cylinder bore above the top-dead-centre position of the piston andbelow the cylinder head, the fuel introduced into the combustion chambercontacting the catalyst and mixing with the air compressed in thecylinder during the preceding compression stroke, so that the air/fuelmixture is ignited by the catalyst and passes through the catalytic discto complete the combustion.

With such an arrangement, however, the presence of the relatively thickcatalyst member in the cylinder bore between the piston crown and thecylinder head is likely, in a practical design of engine, to impose aserious restriction on the possible value of the compression ratio, ifmechanical interference is to be avoided. A low compression ratio leadsto unacceptably low thermal efficiency and fuel economy. Moreover, sincethe effect of the use of the catalyst for ignition is to permitoxidation of the fuel, i.e. combustion, at weaker mixture strengths thancan be used with conventional forms of ignition, it would be desirableto take advantage of this to utilise higher than normal compressionratios without "knock" in conjunction with air/fuel mixturesspecifically weaker than that for stoichiometric mixture strength.

BRIEF SUMMARY OF THE INVENTION

According to the parent invention, an internal combustion engine ofreciprocating-piston type has in each cylinder a combustion chamber themajor portion of the volume of which, at the top-dead-centre position ofthe piston, is afforded by a recess formed in the upper surface of thepiston crown, and is provided with a catalytic element carried by thepiston and mounted in a position in which at least a part of thecatalytic element overlies the said recess, and means is provided forinjecting fuel into the recess when the piston is at about itstop-dead-centre position and in a direction such that substantially thewhole of the injected fuel will contact the surface of the catalyticelement to initiate its combustion.

The catalytic element may for example be formed with multiple smallapertures or passages extending through its thickness, through which theinjected gaseous or atomised-liquid fuel will pass, and may extendcompletely across the open top of the recess. For example the elementmay be of a gauze, matrix or mesh structure, or may be a porous orperforated sheet or a sintered member.

By means of the invention the presence of unburnt hydrocarbons in theexhaust emission can be greatly reduced or even avoided altogether. Atthe end of the compression stroke or stage, the gas pressure andtemperature and the amount of oxygen present are much more favourablefor catalytic oxidation of the hydrocarbons than is the case in acatalyst box situated within the engine exhaust system as in knownarrangements. Furthermore, stratification of the charge is not requiredbecause a homogeneous lean mixture of almost any air/fuel ratio can beoxidized catalytically by means of the invention. The engine load can besimply regulated by the amount of fuel supplied to the engine.

The invention can be utilized with engines employing methyl or ethylalcohols, or even gaseous fuels, as well as with petrol and dieselengines, and is particularly advantageous if "wide-cut" fuels have to beused as may become increasingly necessary in the future.

In an example, the or each catalytic element may take the form of abasket structure associated with the combustion recess in the crown ofthe piston, the fuel being injected through a hole in the top wall ofthe basket into the interior of the recess so as to be carried throughthe wall of the basket structure by the movement of the combustion air.

The essential feature of the invention is the use of a catalyst mountedon the piston to overlie the combustion recess in the piston crown, topromote combustion of the fuel at widely-distributed points and at allmixture strengths. For this purpose it is necessary to utilize catalyticmaterial in a structure which has a widely-distributed surface area intointimate contact with which all the fuel to be combusted in the cylindermust be brought so as to ensure multi-point oxidation of all the fuelbefore it reaches the exhaust. Thus the spread of a flame front is notrelied upon to ensure complete combustion of all the fuel.

Catalytic oxidation of an air/fuel mixture may take place attemperatures considerably lower than in conventional flame propagation,and may also occur at air/fuel ratios considerably greater than arenormally used in i.c. engines, and with correspondingly lower heatrelease and temperature rise.

The invention may be carried into practice in various ways, but onespecific embodiment and certain modifications thereof will now bedescribed by way of example only, and with reference to the accompanyingdrawings in which:

FIG. 1 is a sectional elevation of a typical cylinder arrangement in agasoline engine of the fuel-injection kind, indicating the position ofthe fuel injection nozzle at top-dead-centre;

FIG. 1A is a plan view of the piston of FIG. 1;

FIGS. 2 and 2A are views similar to FIGS. 1 and 1A of a modified form ofpiston embodying the invention; and

FIG. 3 is a sectional elevation of another modified piston embodying theinvention.

In the embodiment shown in FIGS. 1 and 1A, a possible form ofdirect-injection petrol engine has a cylinder block 10 and cylinder head11 with poppet valves 11A, 11B all of conventional form, and has pistons12 in the cylinders 13 each of the pistons 12 being provided (as iswell-known for pistons of compression-ignition engines) with acylindrical open-topped recess 14 in the upper side of the piston crown15, the recess 14 forming the major part of the combustion chamber inthe associated cylinder 13 when the piston is in the top-dead-centreposition. Whilst in FIG. 1 the recess 14 has a flat bottom, it ispossible for the recess to have a central circular-section protrusion,e.g. of generally conical form, projecting upwardly in its bottom toform an annular space between itself and the cylindrical side wall ofthe recess along which the air/fuel charge will flow around theprojection.

The engine has associated with each cylinder 13 a fuel injector 16mounted in the cylinder head 11 centrally with respect to the recess 14,the tip of the nozzle 17 of each injector 16 protruding downwardlyslightly into the upper part of the recess 14 at top-dead-centre asshown in FIG. 1. The injector nozzle 17 is supplied with a meteredquantity of gasoline fuel through the associated injector body 16 and apipe (not shown) leading from an injection pump in a conventionalmanner. The nozzle 17 has two delivery holes arranged indiametrically-opposite positions in the nozzle tip so as to spray twojets 18 of atomised fuel in radial, downwardly-inclined directions intothe recess 14.

Air is induced or blown into the engine cylinder 13 above the pistoncrown 15 in one of many known ways in such a manner as to set up arotary motion of the air flow around the cylinder axis in the combustionchamber. This rotary air flow is frequently referred to as air swirl.

Fixed by means of a mounting ring 19 and screws 20 to the piston crown15 to extend across the top of the recess 14 is a circular disc 21 ofwire gauze having a small central hole 22 through which the tip of theinjector nozzle 17 projects with clearance at top-dead-centre, as shownin FIG. 1.

Extending diametrically across the recess 14 between the underside ofthe gauze disc 21 and the bottom of the recess 14, to which its loweredge conforms, is a further sheet 23 of wire gauze which is clamped atopposite ends between the two halves 24A, 24B of a split cylindricalliner 24 which fits closely within the recess 14. The upper edge 25 ofthe vertical gauze 23 is reinforced against inertia forces by a wire 26.

The liner halves 24A, 24B are secured together by means ofcircumferentially-extending screws 27. The vertical gauze sheet 23 thusdivides the recess 14 within the liner 24 into two semi-cylindricalspaces, into which the two fuel jets 18 are respectively sprayed by theinjector nozzle 17 as shown in FIG. 1A. The upper edge 25 of the gauze23 has a small cutaway 28 to accommodate the tip of the nozzle 17.

Injection of the fuel from the nozzle 17 takes place through the centralhole 22 in the top gauze 21 into the recess 14, starting shortly beforethe top-dead-centre position is reached.

It will be seen from FIG. 1A that the two jets 18 of sprayed fuel aredirected into the respective spaces in the recess 14 near the portionsof the vertical gauze 23 which are respectively upstream of the jets 18with respect to the direction of air swirl around the recess indicatedby the arrow A (FIG. 1A), so as to allow time for fuel vapourizationbefore the air swirl carries the atomised and vapourised fuel onto thedownstream portions of the gauze 23. The air flow of course passesfreely through the material of the gauzes 21 and 23.

The gauzes 21 and 23 are made of or coated with a suitable catalyst forcombustion. For example the gauzes 21 and 23 may be made of platinumwire, or of a suitable heat-resistant wire which has been coated eitherwith platinum by electroplating, or with a suitable thin wash of aporous heat-resisting ceramic on which the platinum ischemically-deposited in a known manner so as to have a large surfacearea. Instead of pure platinum, use may be made of some other catalyticmaterial, for example a metal with a specially treated surface, or oneof the known combinations with platinum of small quantities of otherelements (mostly confined to the same chemical group as platinum) whichenhance the catalytic action of pure platinum.

It will be understood that as the fuel, i.e. petrol, is sprayed into thesemi-cylindrical spaces within the recess 14 below the top gauze 21 andon either side of the diametrical gauze 23, the atomized fuel will betaken up by the air swirl and carried into contact with one or each ofthe catalytic gauzes 21 and 23 by which it will be ignited. The whole ofthe air flow into which the fuel has been injected must pass through atleast one of the catalytic gauzes before it can escape from the recess11 into the adjacent cylinder space, and this ensures multiple-pointcatalytic oxidation of the whole of the fuel before it can reach thecylinder exhaust port, so that virtually no unburnt hydrocarbons will bepresent in the exhaust gases.

If the injector nozzle 11 has more than two injection holes, the singlediametral gauze 23 will be replaced by a corresponding number of radialgauze sheets. For example, with an injector nozzle having four sprayholes delivering radial jets of fuel at 90° spacings, thecatalyst-carrying structure will have four radial gauze sheets extendingbelow the top gauze 21 to divide the internal space in the recess 14into four quadrants, into which the fuel jets 18 are respectivelysprayed.

FIGS. 2 and 2A show a modified construction of the piston assembly ofFIGS. 1 and 1A, in which the catalyst-carrying structure comprises apressed or spun sheet metal bowl 35 which is a close fit in the recess14' and whose bottom wall is clamped to the bottom of the recess bymeans of a clamping bolt 36 extending through a hole in the piston crown15', the hole being lined by a sleeve 37. The head of the bolt 36overlies and is welded to a clamping plate 38 which in turn overlies andis welded to the bottom wall of the bowl 35, so that the whole assemblyof bowl 35, clamping plate 38 and bolt 36 forms a unitary structure. Anut 39 threaded onto the bolt 36 below the piston crown bears againstthe sleeve 37 which acts as a spacer, and a stack of Belleville washers40 threaded onto the stem of the bolt 36 is interposed between the nut39 and the under surface of the piston crown 15' to hold the unitarybowl structure firmly to the bottom of the recess 14' in a mannerpermitting differential thermal expansions of the various components.

The top gauze 21' comprises a disc of wire gauze which is strengthenedby a spider 41 with inner and outer wire reinforcing rings 42 and 42A,and is secured as by welding beneath the top lip 43 of the pressed orspun bowl 35. The diametral gauze 23', which has a cutout 44 in itslower edge to clear the head of the bolt 36, is held in position bywelds at its edges to the bowl 35 and clamping plate 38. The gauzes 21'and 23' are made of or coated with a catalyst material as before.

FIG. 3 shows another modification in which the catalyst-carryingstructure comprises a pressed or spun sleeve 50 with upper and lowerinwardly-directed lips 51 and 52. The upper gauze 21" is welded to theupper lip 51 at its circumference, and the lower lip 52 is welded to thecircumference of an annular bottom plate 53 held in position by the bolt36 as in the case of FIG. 2. The diametral gauze 23" is welded at itsupper edge to the top gauze 21" and at its opposite ends to the sleeve50.

The operation of the embodiments of FIGS. 2 and 2A and of FIG. 3 issimilar to that of FIGS. 1 and 1A.

It should be pointed out that the practical design considerationsinvolved in the design of adequate inlet and exhaust ports and valvesizes, in conjunction with a generally-central injection position, willusually result in configurations in which the centre of the recess inthe piston crown, and the tip of the injection nozzle, are both slightlyoff the axis of the cylinder bore. The centre of the tip of the nozzle17 and the central axis of the recess 14 etc., are usually not exactlycoincident.

Whilst in the specific embodiments described and illustrated thecatalyst comprises or is carried on metal gauze, it is possible to useother arrangements in which the whole of the fuel in the air/fuelmixture is passed through or over a widely-distributed catalyst in thecombustion chamber before it can reach the exhaust port. For example,instead of gauze it is theoretically possible to use perforated metalsheet coated with catalyst; short pieces of material in matrix formhaving circular, triangular or other geometrically-shaped passagesformed from ceramic, glass or metallic sheet coated with the catalyst;or even sintered porous materials whose surfaces are coated with thecatalyst.

What I claim as my invention and desire to secure by Letters Patentis:
 1. An internal combustion engine of reciprocating-piston type havinga cylinder with a combustion chamber, and a piston with a crown in thecylinder, the major portion of the volume of said combustion chamberbeing afforded by a recess formed in the crown of the piston, the recess.Iadd.having an open mouth at its upper side and .Iaddend.having abottom, a catalytic element .Iadd.of foraminous sheet constructionthrough whose thickness gas can flow freely, said element being carried.Iaddend.in the cylinder .[.carried.]. by the piston, .[.and.]..Iadd.said catalytic element being effective without additional ignitionmeans to initiate combustion of a fuel vapour and air mixture and havinga cover portion extending crosswise of said recess, said cover portionbeing .Iaddend.mounted in a position overlying .Iadd.and spaced from.Iaddend.the bottom of said recess .Iadd.and enclosing a space beneathit within the recess, and said element having at least one portiondepending from said covered portion towards the bottom of said recess,means for introducing combustion air into the combustion chamber,.Iaddend.and means for injecting fuel into .Iadd.said space enclosed bysaid cover portion in .Iaddend.said recess, when the piston is at aboutits top-dead-centre position, .Iadd.in a manner .Iaddend..[.direction.].such that substantially the whole of the injected fuel will .Iadd.travelinto .Iaddend.contact .Iadd.with .Iaddend.the surface of the catalyticelement to initiate its combustion. .[.
 2. An internal combustion engineas claimed in claim 1 in which the catalytic element has a structureformed with multiple apertures extending through its thickness, throughwhich apertures the injected fuel mixed with combustion air passes..].3. An internal combustion engine as claimed in claim .[.2.]. .Iadd.1,.Iaddend.in which the catalytic element is of grid construction.
 4. Aninternal combustion engine as claimed in claim .[.2.]. .Iadd.1,.Iaddend.in which the catalytic element is of matrix construction.
 5. Aninternal combustion engine as claimed in claim .[.2.]. .Iadd.1,.Iaddend.in which the catalytic element is of sintered construction. 6.An internal combustion engine as claimed in claim .[.2.]. .Iadd.1,.Iaddend.in which the catalytic element extends completely across theopen .[.top.]. .Iadd.mouth .Iaddend.of the recess, whereby the fuel/airmixture leaving the recess passes outwardly through the catalyticelement.
 7. An internal combustion engine as claimed in claim 6, inwhich the catalytic element is formed with an aperture through which thefuel is injected into the interior of the said .[.recess.]. .Iadd.space.Iaddend.by the said means for injection.
 8. An internal combustionengine as claimed in claim 7, in which the catalytic element is .[.ofbasket.]. .Iadd.carried by an insert member of bowl .Iaddend.shape.[.and construction and is.]. mounted in the said recess, with the.[.top wall.]. .Iadd.cover portion .Iaddend.of the .[.basket.]..Iadd.element .Iaddend.extending completely across the open top of the.[.recess.]. .Iadd.bowl and with the depending portion projecting downinto the bowl. .Iaddend.
 9. An internal combustion engine as claimed inclaim 8, in which the interior of the .[.basket-shaped catalyticelement.]. .Iadd.bowl .Iaddend.is divided into a plurality ofcompartments by .[.at least one dividing wall extending transversely tothe said top wall and depending therefrom, the dividing wall also beingpermeable to the flow of combustion gas,.]. .Iadd.the said dependingportion, .Iaddend.and in which the said means for fuel injection isarranged to inject fuel through the said aperture separately into eachof said compartments.
 10. An internal combustion engine as claimed inclaim 9, in which the said recess is cylindrical in form and in whichthe .[.basket-shaped catalytic element.]. .Iadd.bowl .Iaddend.is alsocylindrical in form and fits the recess.
 11. An internal combustionengine as claimed in claim 10, in which the said .[.dividing wall.]..Iadd.depending portion .Iaddend.extends diametrically across the.[.basket-shaped catalytic element.]. .Iadd.bowl.Iaddend..
 12. Aninternal combustion engine as claimed in claim .[.9.]. .Iadd.11,.Iaddend.in which there are more than two of the said compartments inthe .[.cylindrical catalytic element.]. .Iadd.bowl .Iaddend.respectivelyseparated by .Iadd.depending portions which are .Iaddend.radial.[.dividing walls.]. .Iadd.with respect to the bowl.Iaddend..
 13. Aninternal combustion engine as claimed in claim .[.2.]. .Iadd.1,.Iaddend.wherein the catalytic element is of gauze construction.
 14. Aninternal combustion engine as claimed in claim .[.2.]. .Iadd.1,.Iaddend.wherein the catalytic element is of mesh construction. .Iadd.15. An internal combustion engine as claimed in claim 1, wherein saidmeans for injecting fuel into said space includes a nozzle projectingthrough said cover portion of said catalytic element into saidspace..Iaddend.